1. Field of the Invention
This invention relates to a method for forming a gate dielectric layer, and more particularly, to a method for treating an oxide layer by using a remote plasma nitridation procedure and a thermal annealing procedure to improve the channel mobility.
2. Description of the Prior Art
The gate dielectric layer is very important in the metal oxide semiconductor field effect transistor (MOSFET). In order to increase the velocity of the elements and shrink the device dimension, the thickness of the gate dielectric layer will become thinner and thinner. As the thickness of the gate dielectric layer decreases more, the requirement for the gate dielectric layer becomes stricter. A good gate dielectric layer must have lower leakage current (as well as higher breakdown field).
When the thickness of the gate dielectric layer becomes thinner, the electric field across of the gate dielectric layer will be increased for a fixed operating voltage. Therefore, a high-quality dielectric layer is needed. There are some methods in checking the qualities of the gate dielectric layer, such as: (1) time-zero dielectric breakdown (TZDB): sweep the voltage level until the leakage current being higher than a value or detecting a current jump; (2) charge to breakdown: adding all the changes going through the dielectric layer during a constant voltage stress until a current jump occurs; (3)time-dependent dielectric breakdown (TDDB): applying several stress voltages to the devices, measuring the time-to-breakdown, and predicting the device lifetime under normal operation condition.
The traditional method for forming the gate dielectric layer is to use the thermal oxidation procedure to form an oxide layer on the substrate. One recent method now used to form the dielectric layer is to use the remote plasma nitrided oxide layer to be the gate dielectric layer. This method can get a higher dielectric constant for the need of the advanced dielectrics.
Referring to FIG. 1, a diagram for forming an in-situ steam generation (ISSG) oxide layer on the substrate is shown. At first, a wafer, which comprises a substrate 10, is provided. This substrate can be silicon substrate. Then an in-situ steam generation oxide layer 20 is formed on the substrate 10. This in-situ steam generation oxide layer 20 is formed by using the wet oxide procedure.
Referring to FIG. 2, the wafer is then placed into the reaction chamber to proceed a remote plasma nitridation procedure. Nitrogen ions 25 are introduced into the in-situ steam generation oxide layer 20 by using the remote plasma nitridation procedure to become a remote plasma nitrided oxide layer 30 (referring to FIG. 3). This remote plasma nitrided oxide layer 30 is used to be the gate dielectric layer. The nitrogen profiles (i.e., concentration and distribution) can be adjusted depending on the needs of different applications.
Although the remote plasma nitrided oxide layer can get a higher dielectric constant, the channel mobility of the remote plasma nitrided oxide layer is degraded. Therefore, this process will decrease the device performance.
In the current procedure to form the remote plasma nitrided oxide layer using the remote plasma nitridation procedure, the in-situ steam generation oxide layer is formed on the substrate using the wet oxide procedure and is then treated using the remote plasma nitridation procedure to form the remote plasma nitrided oxide layer. Therefore, this procedure will also complicate the process steps and hence decrease the production efficiency of the procedure.
In accordance with the background of the above-mentioned invention, the known method for forming the remote plasma nitrided oxide layer will decrease the performance and the reliability of the gate dielectric layer and will decrease the production efficiency. The present invention provides a method for treating an oxide layer by using a remote plasma nitridation procedure and a subsequent thermal annealing procedure to form a gate dielectric layer to get better channel mobility.
The second objective of the present invention is to increase the performance of the gate dielectric layer by using a remote plasma nitridation procedure and a thermal annealing procedure in turn to treat the oxide layer to be used as the gate dielectric layer.
The third objective of the present invention is to increase the reliability of the gate dielectric layer by using a remote plasma nitridation procedure and a thermal annealing procedure in turn to treat the oxide layer to be used as the gate dielectric layer.
The fourth objective of the present invention is to increase the qualities of the semiconductor elements by using a remote plasma nitridation procedure and a thermal annealing procedure in turn to treat the oxide layer to be used as the gate dielectric layer.
A further objective of the present invention is to increase the production efficiency of the semiconductor procedure by using a remote plasma nitridation procedure and a thermal annealing procedure in turn to treat the oxide layer to be used as the gate dielectric layer.
In accordance with the foregoing objectives, the present invention provides a method for forming better qualities of the gate dielectric layer by using a remote plasma nitridation procedure and a thermal annealing procedure in turn to treat the oxide layer as used to be the gate dielectric layer. The first step of the present invention is to form a base oxide layer on a substrate of a wafer. The base oxide layer is an oxide layer, which can be formed using any kind of method. Then nitrogen ions are introduced into the base oxide layer using the remote plasma nitridation procedure to form a remote plasma nitrided oxide layer. At last, thermal annealing using oxygen (O2) or nitric monoxide (NO) is applied to the remote plasma nitrided oxide layer to increase the channel mobility and the performance of the gate dielectric layer of the present invention. The present invention can also increase the reliability of the gate dielectric layer and to increase the qualities of the semiconductor elements. The present invention can further increase the production efficiency of the semiconductor procedure.